Automatic exposure control for camera lens



June 20, 1967 c. A. GREGORY, JR, ETAL 3,327,186

AUTOMATIC EXPOSURE CONTROL FOR CAMERA LENS 8 Sheets-Sheet 1 OriginalFiled Feb. 25, 1965 .4 T J M m v. e V m K m a. c m M G s 0 .m A S m .w CM r M 2 v7 0 /W. m M M ||||.|\J J ||||||u n 3523 T Mafia? A mzmj 1. 3 mmwmm vm on vw w. 2 v 4 J R v 3 x9555 5&3 r wig a: 4 52 333051 mo$ Ewmml52E mwtnrm H 625 3 mm @N NN ATTORNEY June 20, 1967 c. A. GREGORY, JR.ETAL 3,327,186

AUTOMATIC EXPOSURE CONTROL FOR CAMERA LENS 8 Sheets-Sheet 2 OriginalFiled Feb. 25, 1 963 INVENTORS Churfies A. Gregory,J r.&

zwm on x96: N w .J w Eo mwtnzw I mm y) mm 8 3 6.6 ow mm mwFSzm "6.5652.u m: 3m 3024 mwhSxw E 322 28: 553m T v mum mm 52K mm fik wig .38 A 02 3iNu smu mm a m whozwm V t: r w? we 3 d Nm 8 mm 3 $238? R 6 50 w m 22 .m ua z 3 m 3339i mz w 55 Comm mum 205 2%; \H mm .mmm [IL 8 $1. 2 m. moESoum92 555mm E% Malcolm S. McKenney ATTORNEY C. A. GREGORY, .J'R.. ETALAUTOMATIC EXPOSURE CONTROL FOR CAMERA LENS 8 Sheets-Sheet 5 OriginalFiled Feb. 25, 1963 INVENTORS Charles A. Gregory,Jr& Y

FIG. 3. FIG. 30.

ATTORNEY June 20, 1967 c. A. GREGORY, JR, ETAL 3,327,186

AUTOMATIC EXPOSURE CONTROL FOR CAMERA LENS Original Filed Feb. 25, 19638 Sheets-$heet 4 140 "AQJISZ H4 H6 I72 i A scnz 7 I88) I86 I ssT J PI]INVENTORS Charles A.'Gregory,Jr.8 Fl G .30. Malcolm S. McKenney BY Maw/aw ATTORNEY June 20, 1967 Original Filed Feb. 25, 1963 ZIZ C. A.GREGORY, JR. ETAL AUTOMATIC EXPOSURE CONTROL FOR CAMERA LENS 8Sheets-Sheet 5 FIG.

INVENTORS Charles A. Gregory,Jr.& Malcolm S. McKenney BY %m am WATTORNEY June 20, 1967 c. A. GREGORY, JR. ETAL 3,327,186

AUTOMATIC EXPOSURE CONTRQL FOR CAMERA LENS Original Filed Feb. 25, 19658 Sheets-Sheet e 8/ LE NS 'Q- 258 I 200 232 l 206 05 I l l i l I l i/282 I I 288 L am Fl G. 4Q. INVENTORS Charles A. Gregory,Jr.& Malcolm S.McKenney ATTORNEY 8 Sheets-Sheet 7 INVENTORS Charles A.Gregory,Jr.&Mulcoim S. McKenney ATTORNEY June 20, 1967 c. A. GREGORY, JR, ETAL.

AUTOMATIC EXPOSURE CONTROL FOR CAMERA LENS Original Filed Feb. 25, 1963June 20, 1967 c. A. GREGORY, JR. ETAL 3,327,186

AUTOMATIC EXPOSURE CONTROL FOR CAMERA LENS 8 Sheets$heet 8 OriginalFiled Feb. 25, 1963 FEGY.

Maw O r n n W y e r K Ww leM r I G 8 m mm VII 0 0 M C 9 G F BY M/WATTORNEY United States Patent 3,327,186 AUTOMATIC EXPOSURE CONTROL FORCAMERA LENS Charles A. Gregory, Jr., and Malcolm S. McKenney,

Richmond, Va., assignors to Giannini Scientific Corporation, acorporation of Delaware Original application Feb. 25, 1963, Ser. No.260,659, now Patent No. 3,230,847, dated Jan. 25, 1966. Divided and thisapplication Oct. 31, 1963, Ser. No. 327,168

13 Claims. (Cl. 318-28) This is a division of application Ser. No.260,659 filed Feb. 25, 1963, now Patent No. 3,230,847.

This invention relates to automatic exposure control systems for camerasand the like and more particularly, to automatic exposure controlsystems of the electronic servo type.

In determining the proper film exposure for a given lens setting thereare a number of variables to consider. For example, for a given f/numberand corresponding light condition a particular exposure time or shutterspeed is necessary in order to achieve optimum results. This particulararrangement of variable is a somewhat standard approach to setting upthe operating format of various known cameras.

However, in cameras with multiple frame techniques such as those used inaerial photography, the shutter speeds are constant over extendedperiods during which a series of consecutive photographs are beingtaken.

With the exposure time thus held constant,.the only solution whichremains for exposure control is to automatically vary the amount oflight reaching the film. A change in the f/number or f/stop setting ofthe camera lens is therefore in order.

conventionally, the f/stop setting controls the size of the aperture ofan iris diaphragm located in front of a camera lens, the f/number beingan indication of the relative size of the focal length of the lens andthe diameter of the aperture.

Another means for controlling exposure is the use of a constant speedrotary shutter wherein the angle between the shutter blades may bevaried to vary the size of the rotating sector and hence the time ofexposure of the film. It is to the automatic adjustment of the bladeangle in this rotary type shutter to which this invention isspecifically directed. However, automatic adjustment of an irisdiaphragm may also be effected by this invention.

A rotary shutter and means for adjusting same is the subject matter of acopending application to Gregory, Jr., et al., entitled, VariableShutter Mechanism, Ser. No. 156,453, filed Dec. 1, 1961, now Patent No.3,186,003.

Automatic exposure controls, in the past, have been operated based onfunctions of light intensity as the controlling inputs for the varioussystems used. While this type of input function is necessary to achievesome form of automatic exposure control, the output characteristics ofan exposure controlling servo system are not readily adaptable to theformat of the adjustment mechanisms conventionally desired forcameras.

Accordingly, it is an object of this invention to provide an automaticexposure control system wherein the input is a function of lightintensity and the output is a proportional function of the camera lensf/stop numbers, over a givenrange of f/stop numbers, whereby theautomatic adjustment provided is directly adapted to the format of thecamera.

Another object of this invention is to provide an automatic exposurecontrol comprising a photoconductive input transducer and servo meansenergized by said transducer as a function of the intensity of theincident light on said transducer, including feedback means for varyingthe response characteristics of said transducer in response to saidincident light, whereby the response of said automatic exposure controlis proportional to camera lens f/ stop numbers.

Another object of this invention is to provide an automatic exposurecontrol comprising a photoconductive input transducer and servo meansenergized by said transducer as a function of the intensity of theincident light on said transducer including feedback means for varyingthe response characteristics of said transducer in response to saidincident light, whereby the response of said automatic exposure controlis proportional to camera lens f/stop numbers, wherein said feedbackmeans includes a variable resistor in circuit with said photoconductiveinput transducer and means for automatically varying said resistor.

Another object of this invention is to provide an automatic exposurecontrol including a photoconductive input transducer having a separatelens system from that of the main camera lens, the separate lens systembeing provided with the same acceptance angle as the main lens systemand being boresighted to aim in a line parallel to "ice . the centerlineof the main camera lens, whereby the separate lens system sees the samearea as the main camera lens, and further including a selectivelyadjustable iris diaphragm in the separate lens system to thereby biasthe said input transducer for any given camera operating conditions.

Still another object of this invention is to provide an automaticexposure control for cameras incorporating novel null-balance circuitry.

Still another object of this invention is to provide an automaticexposure control for cameras incorporating novel null-balance circuitryadapted to be unbalanced in response to variations in light intensity,and power control servo means proportionally energized in response tothe degree of unbalance thereof to automatically rebalance saidcircuitry and simultaneously vary the shutter setting of a camera as afunction of the f/stop numbers thereof.

These and other objects of this invention will become apparent withreference to the following specification and drawings which relate toseveral preferred embodiments of the invention.

In the drawings:

FIGURE 1 is a general block diagram of the invention;

FIGURE 2 is a more specific block diagram of the invention;

FIGURES 3 and 3a are, taken together, a schematic of one embodiment ofthe invention;

FIGURES 4 and 4a, are, taken together, a schematic of another embodimentof the invention;

FIGURE 5 is a front end view showing the separate lens system andadjusting means for the input transducer of the invention adjacent themain camera structure;

FIGURE 6 is a side elevation of FIGURE 5 with one side of the casingremoved;

FIGURE 7 is a detailed cross-section taken along line 77 of FIGURE 6.

FIGURE 8 is a detailed internal elevation of a portion of FIGURE 5 withthe front cover plate removed; and

FIGURE 9 is a detailed cross-section taken along line 9-9 of FIGURE 8.

I. THE BASIC SYSTEM OF FIGURE 1 The invention may be broadly describedwith reference to FIGURE 1 in which a camera means 10 including avariable rotary shutter means 12 and a primary lens system 14 is shown.

In order to control the degree of exposure of the film in the camerameans 10 by automatically varying the blade angle adjustment of therotary shutter means 12 as described in the said copending applicationsupra, a light sensing and transducer means 16 is provided having aseparate or secondary lens system 18, including selectively variablelight restricting means'(not shown), with an acceptance angle equal tothe acceptance angle of the primary lens system 14. The secondary lenssystem '18 is of the gunsight type and is aimed by boresighting or thelike along a line parallel to the centerline of the primary lens system12, whereby the two lens systems both see the same area and lightconditions.

The light conditions of the area to be photographed are fed to thesensor means 16 from the secondary lens system 18 via an input 20 whichin realityis an optical path.

The output response of the transducer in the sensor means 16 isconnected via an input connection 22 to a null-balance bridge typedetector circuit 24.

A second input connection 26 on the bridge circuit 24 is provided toConnect an output signal indicative of the present adjusted position ofthe variable shutter means 12 to the null-balance bridge circuit 24 tobe compared to the output signal from the sensor means 16.

The output signal from the bridge circuit 24, which is proportional tothe unbalance generated therein in response to the differential in thesignal representative of actual light conditions in the area to bephotographed and those for which the shutter means 12 is set, in fedthrough an input connection 28 to a servo amplifier 30.

The output response of the amplifier 30 is a control signal which is fedthrough an input connection 32 to the control means (not shown) of avariable shutter drive and adjustment means 34 which is drivablyconnected with the variable shutter means 12 by means of a connectiongenerally indicated as an input 36.

A servo loop is thus established which begins with the null-balancebridge circuit 24 and progresses through the servo amplifier 30, ashutter drive means 34 and variable shutter means 12, back to the saidbridge circuit 24.

Operating power for all of the operational elements of the servo loop issupplied from a power supply 38 via power connections 40, 42 and 44 tothe bridge circuit 24, amplifier 30 and shutter drive means 34,respectively.

The system of the invention having been broadly set forth, the means forproviding the automatic control of the rotary shutter means 12 of FIGURE1 by means of the servo loop defined in the description of that figure,are more specifically illustrated in FIGURE 2 and will now be described.

II. THE EMBODIMENT OF FIGURE 2 Referring now to FIGURE 2, wherein likenumerals to FIGURE 1 indicate like elements, the sensor means is shownas comprising a photoconductive device 16F and a thermoelectrictemperature compensating means 16T therefore, interconnected asgenerally indicated by the connection 46.

The output of the photoconductive transducer 16F is introduced to theservo loop at the first input 22 of the bridge circuit 24 and theresulting response of the said bridge circuit is fed to the input 28 ofthe servo amplifier 30.

The amplifier output is fed to the input 32 of a control circuit 34C inthe variable shutter control means which means further comprises asilicon controlled rectifier (SCR) power regulator gate 34R controlledby the control circuit 34C, and a shutter drive motor 34M selectivelyenergized by the power gate 34R.

The output of the control circuit 34C comprises a gating control pulse,to be hereinafter more fully described as to its derivation, which isfed to the input 48 of the SCR power gate 34R.

The regulated power output of the SCR power gate 34R is fed to theshutter drive motor 34M via a connection 50. As generally indicated inFIGURE 1, the output of the drive motor 34M is connected via a coupling36 to the shutter means 12. As specifically shown in FIGURE 2, thecoupling 36 extends between the drive motor 34M and the variable shuttermechanism 125 of the shutter means 12.

The shutter means 12 further comprises an output cam drive 12D, coupledto the variable shutter mechanism 12S a connection 52 and thus driven bymotor 34M, and a feedback potentiometer 12F coupled via a connection 54through the cam drive 12D and connection 52 to the shutter mechanism12S, whereby the said feedback potentiometer is adjustably positioned inresponse to the adjusted position of the variable shutter mechanism.

The output of the feedback potentiometer 12F provides the necessaryerror signal for the servo loop and is applied to the second input 26 ofthe null-balance bridge circuit 24.

The power supply is shown as comprising a power transformer 38T feedingthe null balance bridge circuit 24 via a first rectifier and regulatormeans 38R and power lead 40 and feeding both the servo amplifier 30 andthe control circuit 34C via power leads 42 and 56, respectively. Aseparate lead 58 is provided directly from the transformer,38T to theSCR power gate 34R.

Further refinements over the general system of FIG- URE 1 are the use ofa remote reading shutter adjustment indicator '60 and a mechanicallydriven local shutter adjustment indicator 62. The remote indicator 60 isconnected to an output of the bridge circuit 24 via a suitable lead 64.The local indicator 62 is mechanically coupled to the shutter mechanism125 via a connection 66.

As indicated by the arrow 68, a sunshade may be provided for the inputside of the secondary lens system 18. The use of a variable densityoptical filter positioned between the secondary lens system 18 and thephotoconductive transducer 16P, as indicated by the arrow 70, may alsobe desired.

III. THE EMBODIMENT OF FIGURE 3 Reference is now made to FIGURE 3 wherea detailed schematic of one embodiment of the block diagram of FIGURE 2is shown.

The secondary lens system 18 is generally indicated as including anadjustable iris diaphragm 18A therein for controlling the degree ofillumination of the photoconductive transducer 16F. In a preferredembodiment of the invention a cadmium sulphide cell is used as thetransducer 16P.

Temperature compensation is provided for the transducer 16P by athermistor 1-6T connected in series with the transducer via a commonintermediate junction 72.

(A) The bridge circuit The bridge circuit 24 includes a pair of powerinput terminals 74 and 76 and a pair of signal output terminals 78 and80 arranged, respectively, on alternate diagonals of the bridge circuit24. First and second fixed value bridge arms comprising fixedresistances '82 and 84 are provided on either side of the second outputterminal 80 and are respectively connected from the terminal 8 to thefirstand second power input terminals 74 and 76.

The thermistor 16T is connected in shunt with a fixed resistor 86forming an integral part of a third bridge arm comprising additionalseries connected variable bias resistor 88 and fixed resistor 90, thesaid third arm extending between the first signal output terminal 78 andthe first power input terminal 74 in the order described.

The common junction 72 between the photoconductive transducer 16P andthe thermistor 16T is coincident with the first signal output terminal78. The transducer 16P forms an integral part of the fourth arm of thebridge circuit 24 which comprises an illumination response slope controlvariable resistor 92 and a fixed resistor 94 in series therewith,connected in shunt across the photoconductive transducer 16P, andconnected from the first signal output terminal 78 through a portion ofthe resistance element 96 and the variable tap 98 of the feedbackpotentiometer 12F (FIGURE 2) to the second power input terminal 76. Thefeedback potentiometer 12F is thus an integral part of the fourth arm ofthe bridge circuit 24.

Power is supplied to the bridge circuit 24 via leads P1 and P2 connectedto the power input terminals 74 and 76, respectively, the said leads P1and P2 extending to a rectifier regulator circuit 38R connected across afirst secondary winding 99 of the power transformer 38T.

(B) The servo amplifier and control circuit As was generally indicatedin FIGURE 2, and now to be specifically described with reference toFIGURE 3, operating power for the amplifier 30 and control circuit 34Cis provided via a regulator and rectifier 38R. This is shown ascomprising a full wave rectifier 100 having a series connected resistor102 and a pair of Zener diodes 104 and 106 connected in series acrossthe output diagonal thereof. The junction 108 common to the resistor 102and the first Zener diode 104 forms one bias reference terminal whilethe junction 110 common to the two Zener diodes 104 and 106 forms thesecond bias reference terminal for the servo amplifier 30 and controlcircuit 34c. A first output voltage of the regulator-rectifier 38R isthus taken across the first Zener diode 104. A load resistor 112 isprovided in shunt with the first Zener diode 104 for purposes ofstability.

A third bias reference terminal 114 is provided via a series connectedsensitivity control variable resistor 116 and fixed resistor 118connected to the terminal 120 common to the second Zener diode 106 andthe rectifier 100. Thus, a second output voltage of therectifier-regulator 38R is taken across the second Zener diode 106 andis adapted to be selectively variable via the sensitivity controlresistor 116.

The amplifier 30 is shown as comprising a first NPN transistor Q havingbase, emitter, and collector terminals 120, 122 and 124, respectively,and a second NPN transistor Q having base, emitter, and collectorterminals 126, 128 and 130, respectively.

The collector terminals 124 and 130, respectively, of the first andsecond transistors Q and Q are respectively connected to a first commonlead 132 at the potential of the first bias reference terminal 108 viadropping resistors 134 and 136.

The base terminals 120 and 126, respectively, of the first and secondtransistors Q and Q are respectively connected to the first signaloutput terminal 78 of the bridge circuit 24 and a second common lead 138at the potential of the sec-0nd bias reference terminal 110, whichcoincides with the second output signal terminal 80 of the bridgecircuit 24. Thus, the base terminals 120 and 126 of the first and secondtransistors Q and Q cornprise the input terminals of the servo amplifier30.

The emitter terminals 122 and 128, respectively, of the first and secondtransistors Q and Q are connected to a third common lead 140 at thepotential of the third bias reference terminal 114.

The control circuit 340 for the silicon controlled rectifier power gate34R is shown to include first and second unijunction transistors Q and Qrespectively associated with the said first and second transistors Q andQ of the amplifier 30. The first unijunction transistor Q includesemitter and first and second base terminals 142, 144 and 146,respectively, and the second unijunction transistor Q includes emitterand first and second base terminals 148, 150 and 152, respectively.

The emitter 142 of the first unijunction transistor Q is connecteddirectly to the collector 124 of the first NPN transistor Q and througha capacitor C to the second common bias lead 138.

The emitter 148 of the second unijunction transistor Q; is connecteddirectly to the collector 130 of the sec 0nd NPN transistor Q andthrough a capacitor C to the second common bias lead 138.

The respective first base terminals 144 and 150 of the first and secondunijunction transistors Q and Q; are connected, respectively, viadropping resistors 154 and 156 to the first common bias lead 132. Therespective second base terminals 146 and 152 of the first and secondunijunction transistors Q and Q; are connected, respectively, throughthe primarys windings 158 and 160 of first and second outputtransformers T and T to the second common bias lead 138.

The output signals generated by the control circuit 34C, as will behereinafter more fully described, are transmitted to the siliconcontrolled rectifier power gate 34R via the secondaries 162 and 164 ofthe first and second output transformers T .and T respectively.

('C) The silicon controlled rectifier power gate The SCR power gate 34Ris shown as comprising first and second silicon controlled rectifiersSCR1 and SCR2, each having, respectively, the usual anode electrodes 166and 168 and cathode electrodes 170 and 172 of conventional rectifiersand each having a grid or control electrode 174 and 176, respectively.The controlled rectifiers are connected in back-to-back fashion (i.e.,anode-to-cathode) with the common junction between anode 166 and cathode172 being connected directly to one side 178 of a second secondarywinding 180 of the power input transformer 3ST. The common junctionbetween the anode 168 and cathode 170 comprises one terminal 182 of theshutter drive motor 34M, the other terminal 184 thereof being connecteddirectly to the other side 186 of the said second secondary winding1800f the power input transformer 3ST via a lead 188.

The SCR power, gate is thus connected to gate direct current ofcontrolled magnitude and direction through the shutter drive motor 34Mas will be hereinafter more fully described.

The shutter drive motor is shown as comprising a capacitance type D.C.motor having a capacitance network C connected across its terminals.

The secondary 162 of the first output transformer T of the controlcircuit 340 is shunted by a load resistor 190 and connected across thecontrol-electrode 174 and cathode 170 of the first controlled rectifierSCR1. The secondary 164 of the second output transformer T of thecontrol circuit 34C is shunted by a load resistor 192 and connectedacross the control electrode 176 and cathode 172 of the secondcontrolled rectifier SCRZ. The means for selectively gating electricpower through the SCR power gate 34R is thus provided.

The servo loop of the invention is completed by the mechanical drivecoupling 52 (also shown in FIGURE 2) indicated as a broken line'betweenthe shutter drive servo motor 34M and the cam 194 of the cam drive means12D and the drive coupling 54 (also shown in FIGURE 2) indicated as abroken line between the said cam 194 and the movable tap 98 on thefeedback potetniometer 12F in the bridge circuit 24.

IV. THE EMBODIMENT OF FIGURE 4 Referring now to FIGURE 4, an additionalembodiment of the invention is shown which requires a substantiallylesser number of components to effect the automatic exposure controldesired than indicated in FIGURES 2 and 3. In. the description of thisembodiment, like numbers to FIGURES 1, 2 and 3 have been used togenerally designate like and functionally equivalent parts.Specifically, these elements are the secondary lens system 18, theadjustable iris 18A, the photoconductive transducer 16P, the thermistor16T, the feedback potentiometer 12F, the bridge circuit 24, theamplifier 30, the SCR control circuit 340, the SCR power gate 34R andthe shutter drive motor 34M.

7 (A) The bridge circuit In this embodiment the null balance bridgecircuit 24 is of the alternating current type and includes a pair ofpower input terminals 196 and 198 and a pair of signal output terminals200 and 202.

The first and second arms of the bridge 24 comprise, respectively, firstand second equal inductors 204 and 206 connected, respectively, betweenthe first power input terminal 196 and first signal output terminal 200and the said first output 200' and the second power input terminal 198.The first signal output 200 comprises the center tap of a secondarywinding 208, composed of the two inductors 204 and 206, of a first powerinput transformer 210 connected to a suitable AC. power source 212 via apair of leads 214 and 216.

The third arm of the bridge circuit 24 comprises the thermistor 16Tconnected in series with a variable bias resistor 218 and a fixedresistor 220 extending in the order described from the second powerinput terminal 198 to the second signal output terminal 202.

The fourth arm of the bridge circuit 24 comprises photoconductivetransducer 16P shunted by an illumination response slope controlvariable resistor 222, this combination being in series with a portionof the resistance 224 of the feedback potentiometer 12F. The variabletap 226 of the feedback potentiometer 12F coincides with the secondsignal output terminal 202 to define one end of the said fourth bridgearm which is terminated at its other end by the first power inputterminal 196.

(B) The servo amplifier and control circuit The servo amplifier 30 isshown as comprising a single PNP transistor Q having base, emitter andcollector terminals 228, 230 and 232, respectively. The base terminal228 is connected directly to the first signal output terminal 200 of thebridge 24 via a lead 234.

A first common bias lead 236 is provided for both the amplifier 30 andthe SCR control circuit 340, which extends from the second output signalterminal 202 of the bridge 24 to a first bias terminal 238 of a pair ofbias supply terminals 238 and 240. The emitter 230 of the transistor Q;is connected via a dropping resistor 242 to the first bias lead 236. Theamplifier input circuit across the two signal output terminals 200 and202 of the bridge 24 includes a sensitivity controlling variableresistor 244 and a diode 246 connected in parallel between the firstbias lead 236, at the potential of the second output signal terminal202, and the base input lead 234 of the transistor Q the anode of thediode 246 being at the potential of the base terminal 228 of thetransistor Q and, consequently the potential of the first output signalterminal 200. i

The SCR control circuit 34C comprises a single unijunction transistor Qhaving an emitter terminal 248 and first and second base terminals 250and 252, respectively. The first base terminal 250 is connected to thefirst common bias lead 236 via a dropping resistor 254. The second baseterminal 252 is connected to the second bias supply terminal 240 via asecond bias lead 256.

The input to the control circuit 340 from the servo amplifier 30 istaken from the collector terminal 232 of the transistor Q through aninput resistor 258 connected between the said collector terminal 232 andthe emitter terminal 248 of the unijunction transistor Q The outputcircuit for the control circuit 340 comprises a capacitor C connected inseries with a primary winding 260 of an output transformer T3, andextending from the emitter terminal 248 of the unijunction transisor Qand the second bias lead 256.

(C) The silicon controlled rectifier power gate The SCR power gate 34Ris shown as comprising a full wave rectifier bridge 262 having a siliconcontrolled rectifier SCR3 connected across one diagonal thereof,

8 the anode 264 of the controlled rectifier SCR3 comprising a firstterminal on the bridge 262 and the cathode 266 of the controlledrectifier SCR3 comprising a second bridge terminal.

The controlled rectifier SCR3 is provided with a control or gridterminal 268. The input to the controlled rectifier SCR3, whereby theSCR power gate 34R is controlled, is provided by connecting thesecondary 270, of the output transformer T3 in the control circuit 34C,across the cathode 266 and control electrode 268 of the controlledrectifier SCR3. I

The opposite diagonal terminals 272 and 274 of the rectifier bridge 262are connected in one side of the power input circuit of the shutterdrive motor 34M, the first terminal 272 being connected to one side of asecondary Winding 276 of a power transformer 278 at the power source 212via a lead 280, and the second terminal 274 of the rectifier bridge 262being connected via a lead 282 to one side of the shutter motor 34M andthence, through the said motor 34M and a lead 284 back to the other sideof the said secondary 276 of the power transformer 278. A stabilizingresistor 286 is also shown connected across the motor 34M between theleads 282 and 284.

The servo loop of this embodiment is completed through a mechanicalconnection 288, indicated as a dotted line, between the motor 34M andthe movable tap 226 of the feedback potentiometer 12F in the bridgeclrcuit 24.

To complete the description of the power supply cir cults, the biassupply for the amplifier 30 and control circuit 34C comprises a fullwave rectifier bridge 290 connected directly to the power source 212 viaa pair of diagonally disposed input terminals 292 and 294 and arespective pair of leads 296 and 298.

The opposite pair of diagonally disposed terminals, 300 and 302, in therectifier bridge 290, are connected, respectively, to the first biasterminal 238 via a dropping resistor 304 and directly to the second biasterminal 240. A Zener diode 306 and load resistor 308 are connected inparallel across the said bias terminals 238 and 240 to complete the biassupply circuit.

V. THE SENSOR AND SHUTTER ADJUSTMENT MEANS Referring now to FIGURES 5, 6and 7, the mechanical arrangement and interconnection with respect tothe variable shutter means 12, the primary lens system 14, the secondarylens system 18, the photoconductive transducer 16P, the shutter drivemotor 34M and the feedback potentiometer 12F will now be described.

As shown in FIGURE 5, an index dial 310 comprising a rotatable knob 312mounted over a fixed dial plate 314 having a plurality of index markingsthereon as shown, is mounted on the face of a control housing 316. Thespacing between the index markings is logarithmically varied as will behereinafter more fully described.

The index dial 310 is mounted directly below the secondary lens assembly18 which also protrudes from the face of the control housing 316.

As shown in FIGURE 6', the knob 312 of the index dial 310 is mounted onone end of a shaft 318 which extends through a suitable journal (notshown) in the dial plate 314 and terminates in a concentrically mounteddrive pulley 320. An endless drive belt or cable 322 extends from thedrive pulley 320* to a driven pulley 324 concentrically mounted withrespect to a portion of the secondary lens system 18. This provides ameans whereby the secondary lens system may be selectively adjusted toregulate the intensity of the light transmitted therethrough.

Referring now to FIGURE 7, the secondary lens system 18 is shown, incross-section, as including an adjustable iris diaphragm light valve 326internally concentric with and adjusted by the driven pulley 324. The

photoconductive transducer MP is also shown as being physically mountedin the inner end of the hollow tube 328 housing the secondary lenssystem 18.

Referring again to FIGURES and 8, the control housing 316 is shownannexed to a main camera housing 330 having an L-shaped integral housingportion 332 partially enveloping the primary lens assembly 14 whichencloses the variable shutter means 12, the shutter drive motor 34M, camdrive 12D, cam 194, and the feedback potentiometer 12F.

As shown in FIGURE 6, the amplifier and other control circuitry of theinvention, such as described in FIGURES 2 and 4, are housed in thecontrol housing 316 in the form of a prefabricated circuit packagegenerally indicated at 334, suitable electrical leads, not shown, beingconnected with the shutter drive motor 34M and the feedbackpotentiometer 12F in the main camera housing 330.

Referring now in more detail to FIGURE 8 and concurrently to FIGURE 9,the shutter drive servo motor 34M is shown mounted in a bracket 336 andconnected to drive a worm gear 338 integral with its armature shaft 340.

The worm gear 338 drives a spur gear 342 to thereby drive the variableshutter mechanism 12 and adjust the shutter means therein as fullydescribed in the aforementionedcopending application to Gregory, Jr., etal., Ser. No. 156,453, filed Dec. 1, 1961, now Patent No. 3,186,003.

As also shown in FIGURE 9, the spur gear 342 is rotatably journalled ona fixed bearing shaft 344 mounted in the back wall 346 on the L-shapedhousing portion 332. A cam drive pinion 348 is also rotatably journalledon the shaft 344 and is made substantially integral with the sector gear342 by means of splines 350, whereby the said cam drive pinion 343 iseffectively driven by the worm gear 338 (not shown in FIGURE 9).

The remainder of the cam drive 12D includes a second fixed bearing shaft352 mounted in the housing wall 346. Rotataibly journalled on the secondshaft 352 is'a driven pinion 354 intermeshed with the cam drive pinion348 and integrally keyed to the cam 194 which is also journalled on thesaid second shaft. A spacer block 356 and integral instrument dial plate358 for the mechanical shutter angle indicator 62 (also shown in FIGURE2) are fixed to the cam 194 by a spline or screw 360. The indicator 62is completed by attaching a meter pointer 362 to the free tip of thesecond shaft 352.

' The feedback potentiometer 12F may now be driven by means of anelongated rod-like cam follower 364 having a compression spring 366extendingfrom a shoulder 368 on the potentiometer 12F concentric withthe follower 364 to the follower head 370 which isin engagement with thecam 194.

- VI. OPERATION Referring first to FIGURES 5, 6 and 7, the index dial310 has been described as controlling an iris diaphragm 326 or the likewhich regulatesthe amount of light reaching the photocell 1GP, wherebythe automatic exposure control described hereinbefore may :be biased fora particular set of operating conditions for the camera (FIGURE 1).These operating conditions are a combination of a particular film speed,camera frame rate, and the f/stop setting of the primary lens systems14. Each major. scale division on the fixed dial'plate 314 of the indexdial 310 corresponds to a photographic f/ stop, each of which changesthe light admitted through a particular lens by a-factor of 2, thusrequiring logarithmic scaling of the seven (7) major f/stop division onthe said dial plate 314. r

By turning the rotatable knob 312 of the index dial 310 to a higherf/stop number on the dial plate 314, the iris diaphragm 326 is closedfurther to decrease the intensity level of the light impinged on thephotocell 16Pby the secondary lens system 18. As will be hereinafterdescribed,- this creates an unbalance in the automatic control systemwhich causes a change in the blade angle setting of the variable rotaryshutter means 12 in the primary lens system 14. A rotation of the knob312 to a lower f/stop number on the dial plate 314 produces an oppositeresult, increasing the light on the photocell 16F and increasing theshutter angle in the variable shutter means (A) Operation 0 FIGURE 1Referring now to FIGURE 1, once the index dial 310 has been set for thedesired operating parameters of the camera 10, a change in illuminationin the area to be photographed is detected by the gunsight secondarylens 18 and impinged on the photocell 16P, thus creating an impedancechange in the photocell 16P which unbalances the bridge or bridge nulldetector 24. An output signal representative of the magnitude anddirection of the un balance with respect to the standard prescribed bythe initial setting of the index dial 310 is derived from the bridgecircuit 24 by the amplifier 30 and applied, via the input 32, to theshutter drive means 34.

The shutter drive means 34 then responds to the output signal from theamplifier 30 to vary the shutter angle in the variable shutter means 12.This shutter variation causes a feedback signal to be generated andapplied, via lead 26, to the bridge circuit 24, whereby, whenthe-shutter angle of the variable shutter means 12 is properly adjustedto the condition of illumination in the area to be photographed, thebridge 24 will be balanced and the servo system comprising the automaticexposure control will be at a null in its operation. The system willseek, constantly, to vary the shutter angle in the shutter means 12 inresponse to changes in illumination in the area to be photographed,hereinafter referred to as the target area.

(B) Operation of FIGURE 2 The operation of the more complex embodimentof FIGURE 2 will now be described.

Assuming again, an initial f/ stop setting of the index dial 310 for aparticular optimum light condition in the target area as correlated tothe particular. operating parameters of the camera, a change in theillumination of the target area from the optimum reference will cause animpedance change in the photocell MP and a resulting unbalance in thebridge circuit 24.

The amplifier 30, via the connection 28, derives an output error signalrepresentative of the magnitude and direction of the bridge unbalancewith respect to the reference null intially determined by the setting ofthe index dial 310 and constrains the SCR control circuit 34C, via theconnection 32, to provide control pulses for the SCR power control gate34R. The control gate 34R, in turn, selectively gates positive ornegative direct current signals, of a magnitude proportional to theunbalance in the system, from the power transformer 3ST to the shutterdrive motor 34 M which controls the shutter angle in the variableshutter 128.

The change in the shutter angle of the variable shutter 128 istransformed into a feedback or error signal by means of a cam drivemeans 12D which constrains a feedback potentiometer 12F to acorresponding impedance value that is varied until the bridge circuit24, via a connection 26, is rebalanced and the servo system of theautomatic exposure control is brought to a null. The changes in theshutter angle may be read out via a mechanically positioned localindicator 62 or an electrically actuated remote indicator 60.

(C) Operation of FIGURES 8 and 9 Once the cam drive 12D has beenenergized by the shutter drive motor 34M in response to any of thevariout embodiments of SCR power gates 34R of the present V ments of theinvention and is best described at this time.

Rotation of the motor 34M results in rotation of the armature shaft 340thereof which turns the integral worm gear 338 in the same direction.This direction of rotation is transmitted to the spur gear 342 and thecam drive pinion 348 splined thereto. The cam drive pinion 348 is inengagement with the driven pinion 354 and integral cam 194, whereby thecam 194 is driven in a corresponding direction by the variable shutterdrive motor 34 M. The local mechanical indicator 62 is drivensimultaneously with the cam 194, the dial plate 358, integral with thecam 194, being driven with respect to a fixed pointer 362.

The contour of the cam 194 is a logarithmic function which causes thefeedback potentiometer 12F to be repositioned, via the cam follower 364,in proportion to f/stop numbers, thus adapting the exposure controlsystem to the operating format of the camera. This becomes clearer whenit is considered that the rotational position of the cam 194 isconstrained to the shutter angle position, a feedback or error signalcalibrated in proportion to f/stops thus being essential for properoperation of the exposure control system.

(D) Operation of FIGURES 3 and 3m Variation in target area illuminationcauses the photoconductive cell 16P, via the secondary lens system 18,to unbalance the bridge circuit 24 causing an unbalance signal voltageto appear across the bridge output terminals 78 and 80 to which the baseterminals 120 and 126, respectively, of the first and second transistorsQ and Q of the amplifier 30 are connected.

The first transistor Q comprises a variable load resistor in arelaxation oscillator circuit, said oscillator comprising the resistor134, capacitor C and the first unijunction transistor Q of the SCRcontrol circuit 340.

The sec-nd transistor Q comprises a variable load resistor in arelaxation oscillator circuit, said oscillator comprising the resistor136, capacitor C and the second unijunction transistor Q of the SCRcontrol circuit 340.

By biasing both of the first and second transistors Q and Q to an ONstate for a balanced condition of the bridge circuit 24, the capacitorsC and C in each of the relaxation oscillator circuits are prevented fromcharging to a sufficient voltage level to trigger the respectiveunijunction transistors Q and Q When an unbalanced condition of thebridge circuit 24 ocurs, however, one of the transistors Q or Q will bebiased to an OFF state, depending on the direction of unbalance and theresulting polarity changes at the output terminals 78 and 80 of thebridge 24, whereby the capacitor C or C respectively, associatedtherewith, will alternately charge and thence dischargethrough itsassociated unijunction transistor, Q or Q, respectively, whereby aseries of trigger pulses will be generated in the second base circuit146 or 152, respectively, of the active unijunction transistor.

The resulting trigger pulses are fed via one of the output transformersT or T to the proper bias or grid terminal 174 or 176 of the first orsecond controlled rectifier SCRI or SCR2, respectively. The triggerpulses, as selectively applied, thus gate direct cur-rent power of aproper polarity through the shutter drive motor 34M to thereby drive thevariable tap 98 of the feedback potentiometer 12F in the properdirection to rebalance the bridge circuit 24, as already described withrespect to FIGURES 8 and 9, causing the oscillations in the controlcircuit 34C to cease and the motor 34M to stop.

If the parmameters of the relaxation oscillators described above areproperly selected such that a full OFF 12 state of the controllingtransistor Q or Q is not required for oscillations to commence, then therepetition rate of the trigger pulses can be varied as a function of themagnitude of unbalance. This would effect the rate of compensationprovided by the shutter drive motor 34M since the average power gated tothe said motor via the SCR power gate 34R could be proportionatelyincreased as a function of the trigger pulse repetition rate.

(E) Operation of FIGURLES 4 and 4a In this embodiment, the variation oftarget area illumination which causes a variation in the impedance ofthe photo-conductive cell 161, creates an unbalance in the bridgecircuit 24 which produces a signal across the output terminals 200 and202 which is shifted in phase, in the direction of unbalance, withrespect to the voltage of the A.C. power source 212, and having amagnitude which is proportional to the amount of unbalance.

The unbalance signal is applied from the base terminal of the transistoramplifier Q which is biased for class B operation, to the common lead236 connected via the bias resist-or 242 to the emitter terminal 242 ofthe transistor Q The bias resistor 242, emit-ter-to-collector path ofthe transistor Q and a coupling resistor 258 connected from thecollector 232 of the said transistor Q, to the emitter terminal 248 ofthe unijunction transistor Q; in the SCR control circuit 34C, comprise aresistive load line controlled by the unbalance signal from the bridgecircuit.

whereby the charging rate of the input capacitor C3 in the SCR controlcircuit 34C is controlled.

Thus, as hereinbefore similarly described with respect to FIGURES 3 and3a, the SCR control circuit 34C comprises a relaxation oscillator whosefrequency of operation is determined by the unbalance signal from thebridge 24 acting through the transistor Q; in the amplifier 30. When thecharge on the capacitor C3 is sufficient to supply the peak voltage tothe emitter 248 of the unijunction transistor Q and bias same into itsnegative resistance region, the capacitor C3 will discharge through theunijunction transistor Q causing the generation of a trigger pulse inthe second base path 252-256 and in the primary 260 of the outputtransformer T3.

Since the SCR control circuit 34R and the bridge circuit 24 are both fedin phase one with the other from the same A.C. source 212, the timing ofthe trigger pulses applied to the grid electrode 268 of the controlledrectifier SCR3 are such as to gate only selected portions of alternatehalf-cycles of A.C. voltage through the rectifier bridge of the SCRpower gate 34R, whereby the magnitude and polarity of the resultingdirect current voltage applied to the shutter drive motor 34M via leads282 and 284 will be proportional to the magnitude and direction ofunbalance in the bridge circuit 24;

The motor 34M, as hereinbefore described with respect to FIGURES 8 and9, drives the variable tap 226 of the feedback potentiometer 12F toadjust the impedance value in that arm of the bridge 24 which containsthe photoconductive cell 16P such that the bridge 24 will be rebalancedand the automatic exposure control system will reach a null.

'In both of the embodiments of FIGURES 3-3a and 4-412, the resistancechange produced in the fourth arm of the bridge 24 by way of temperaturechange of the photocell MP is immediately followed by a like resistancechange in the third arm of the said bridge by means of the thermistor16T whereby no unbalance results over a wide temperature range.

At this point it should be noted that the use of the feedbackpotentiometer 12F as the feedback means of the invention is onlyexemplary. For instance, instead of the potentiometer 12F, a variabledensity light filter (70', FIGURE 2) may be inserted between thesecondary lens system 18 and the photocell 16F and the density thereof,

constrained by the feedback action now exerted by the 13 cam drive 12Don the present potentiometer 12F to thereby vary the effect of theillumination from the target area on the photocell 16P whereby theresistance thereof could be selectively varied to rebalance the bridgecircuit 24.

Another specific feature of the invention with respect to the bridgecircuits 24 is that all feedback actions effect an adjustment in theimpedance in that leg of the bridge 24 where it is initially varied,thus presenting a substantially constant input impedance to theamplifier 30 and providing good stability in the system.

As can be seen from the foregoing specification and drawings, thisinvention provides a new and novel automatic exposure control which isproperly adapted to the operating format of the camera with which it isassociated and which provides a true and rapid response to variations intarget area illumination with a high degree of stability.

It is to be understood that the various embodiments shown and describedherein are for the purpose of example only and are not intended to limitthe scope of the appended claims.

What is claimed is:

1. Servo means for automatically adjusting a first operating parameterin the operating format of a device in response to variations in asecond operating parameter thereof with respect to a preselected optimumreference value of said second parameter comprising, transducer means,means for biasing said transducer means to said optimum reference valueof said second operating parameter, a null balance means including saidtransducer means, said transducer means being responsive to said secondparameter to unbalance said null balance means as a function of themagnitude and direction of the said variations in said second operatingparameter, said null balance means producing an output signal as afunction of the unbalance therein, a trigger generating means, means forcoupling said output signal to said trigger generating means, saidtrigger means producing trigger pulses having a repetition rate which isa function of the characteristics of said output signal, a power source,drive means energized from said power source, a power control gate meansconnected between said power source and said drive means and coupledwith said trigger means whereby power is selectively gated from saidpower source to said drive means by said trigger pulses as a function ofsaid unbalance in said null balance means, said drive means beingconnected with said device to thereby adjust said first operatingparameter, said null balance means including feedback means connectedwith said drive means, whereby said null balance means is rebalanced andsaid servo means is constrained to a null when said first parameter iproperly adjusted with respect to said second parameter.

2. The invention defined in claim 1, wherein said transducer meanscomprises variable impedance means, said impedance being varied as afunction of the variations in said second operating parameter, and saidnull balance means comprises a bridge circuit having said variableimpedance means connected therein.

3. The invention defined in claim 1, wherein said trigger generatingmeans comprises a relaxation oscillator circuit and wherein said meansfor connecting said output signal from said null-balance means to saidtrigger generating means includes a variable load impedance for saidoscillator circuit selectively varied as a function of said outputsignal.

4. The invention defined in claim 3, wherein said variable loadimpedance includes a transistor having a base terminal connected to saidnull-balance means for receiving said output signal and emitter andcollector terminals connected in circuit with said relaxation oscillatorwhereby the emitter-collector impedance of said transistor is varied asa function of said output signal.

5. The invention defined in claim 3, wherein said variable loadimpedance includes a transistor having a base terminal connected to saidnull-balance means for receiving said output signal and emitter andcollector terminals connected in circuit with said relaxation oscillatorwhereby the emitter-collector impedance of said transistor is varied asa function of said output signal and wherein said relaxation oscillatorcircuit includes a unijunction transistor having first and second basecircuits and an emitter circuit, a capacitor connected in said emittercircuit and having a charging rate controlled by said variable impedancemeans in response to said output signal from said null balance means,and a trigger pulse output coupling means in said second base circuit.

6. The invention defined in claim 1, wherein said power control gatemeans includes silicon controlled rectifier means selectively energizedby said trigger pulses from said trigger pulse generating means toselectively gate direct current energy of the proper magnitude andpolarity from said power source to said drive means, said drive meanscomprising a direct current motor and said power source being one ofalternating current.

7. The invention defined in claim 6, wherein said silicon controlledrectifier means comprises a pair of silicon controlled rectifiers havinganode, cathode and control terminals, respectively, said rectifiersbeing mutually connected anode-to-cathode between one side of said drivemeans and one side of said power source, said control terminals of saidrectifiers being connected with said trigger pulse generating means.

8. The invention defined in claim 6, wherein said silicon controlledrectifier means comprises a full-wave diode bridge circuit connectedacross one diagonal thereof from one side of said drive means to oneside of said power source and a silicon controlled rectifier havinganode, cathode and control terminals, said controlled rectifier beingconnected anode-to-cathode across the other diagonal of said diodebridge circuit and having its control terminal connected with saidtrigger pulse generating means.

9. The invention defined in claim 1, wherein said feedback meanscomprises cam means driven by said drive means, follower means driven bysaid cam means, and compensating means, driven by said follower means,acting to oppose the unbalance in said null balance means created bysaid transducer means as said servo means constrains said firstparameter as a function of the variations in said second parameter.

10. The invention defined in claim 9, wherein said cam is provided witha contour functionally related to the said operating format of saiddevice, whereby the compensating action of said compensating means inopposition to said unbalance is correlated to the said operating format.

11. The invention defined in claim 1, wherein said reference meanscomprises calibrated means for selectively varying the response of saidtransducer means to predetermined values of said second operatingparameter, said calibrated means being calibrated as a direct functionof said first operating parameter as represented by the operating formatof the said device.

12. The invention defined in claim 1, wherein said null balance meanscomprises a four arm impedance bridge, said transducer means includes acondition responsive variable impedance means, and said feedback meansincludes a variable compensating impedance means, said conditionresponsive variable impedance means and said variable compensatingimpedance means being connected in the same arm of said bridge, wherebythe impedance presented by said bridge to said means for coupling saidoutput signal to said trigger generating means is a constant.

13. The invention defined in claim 12, wherein said transducer meansincludes a temperature compensating impedance connected in another armof said bridge adjacent said same arm whereby changes in ambienttemperature affecting said condition responsive variable im- 1s pedancemeans are balanced out in said null balance 3,150,303 9/ 1964 James etal 318--28 means. 7 3,181,051 4/1965 Marshall 318-345 References Cited3,191,114 6/1965 Gargani 318-340 X 2724 795 i PATENTS 318 341 5 BENJAMINDOBECK, Primary Examiner.

er X JOHN F. COUCH, 0111s L. RADER, Examiners.

3,003,096 10/1961 Du Bois 318207

1. SERVO MEANS FOR AUTOMATICALLY ADJUSTING A FIRST OPERATING PARAMETERIN THE OPERATING FORMAT OF A DEVICE IN RESPONSE TO VARIATIONS IN ASECOND OPERATING PARAMETER THEREOF WITH RESPECT TO A PRESELECTED OPTIMUMREFERENCE VALUE OF SAID SECOND PARAMETER COMPRISING, TRANSDUCER MEANS,MEANS FOR BIASING SAID TRANSDUCER MEANS TO SAID OPTIMUM REFERENCE VALUEOF SAID SECOND OPERATING PARAMETER A NULL BALANCE MEANS INCLUDING SAIDTRANSDUCER MEANS, PARAMETER TO UNBALANCE SAID NULL BALANCE MEANS AS AFUNCTION OF THE MAGNITUDE AND DIRECTION OF SAID VARIATIONS IN SAIDSECOND OPERATING PARAMETER, SAID NULL BALANCE MEANS PRODUCING AN OUTPUTSIGNAL AS A FUNCTION OF THE UNBALANCE THEREIN, A TRIGGER GENERATINGMEANS, MEANS FOR COUPLING SAID OUTPUT SIGNAL TO SAID TRIGGER GENERATINGMEANS, SAID TRIGGER MEANS PRODUCING TRIGGER PULSES HAVING A REPETITIONRATE WHICH IS A FUNCTION OF THE CHARACTERISTICS OF SAID OUTPUT SIGNAL, APOWER SOURCE, DRIVE MEANS ENERGIZE FROM SAID POWER SOURCE, A POWERCONTROL GATE MEANS CONNECTED BETWEEN SAID POWER SOURCE AND SAID DRIVEMEANS AND COUPLED WITH SAID TRIGGER MEANS WHEREBY POWER IS SELECTIVELYGATED FROM SAID POWER SOURCE TO SAID DRIVE MEANS BY SAID TRIGGER PULSESAS A FUNCTION OF SAID UNBALANCE IN SAID NULL BALANCE MEANS, SAID DRIVEMEANS BEING CONNECTED WITH SAID DEVICE TO THEREBY ADJUST SAID FIRSTOPERATING PARAMETER, SAID NULL BALANCE MEANS INCLUDING FEEDBACK MEANSCONNECTED WITH SAID DRIVE MEANS, WHEREBY SAID NULL BALANCE MEANS ISREBALANCED AND SAID SERVO MEANS IS CONSTRAINED TO A NULL WHEN SAID FIRSTPARAMETER IS PROPERLY ADJUSTED WITH RESPECT TO SAID SECOND PARAMETER.